Two Republican senators are accusing the State Department of misusing taxpayer dollars by green-lighting $500 million for a United Nations climate change program without first obtaining congressional approval.

The senators now are demanding the department justify the "cloak-and-dagger" contribution to the Green Climate Fund (GCF) — even threatening legal action.

"Lawyers cannot replace the constitutional requirement that only Congress can appropriate money," Sen. Cory Gardner, R-Colo., said, adding that he's demanding a "full legal analysis."

Gardner, in a statement to FoxNews.com, alleged the department was trying to "wave a magic wand and write a half-billion dollar check to a Green Climate Fund that they admit was never authorized by Congress."

The Obama administration — despite resistance from congressional Republicans — has committed the U.S. to contributing $3 billion to the fund, a program established by the United Nations to help poor countries adopt clean energy technologies to address climate change.

Along with Gardner, Sen. John Barrasso, R-Wyo., maintains Congress has not allocated any funding for what he calls the "international climate change slush fund" and has in fact "prohibited the transfer of funds to create new programs."

Barrasso said because the GCF technically is a new program and not authorized by Congress, the department may have violated the Anti-Deficiency Act, a law that prohibits federal agencies from obligating or expending funds in advance or in excess of an appropriation.

According to Politico, Barrasso is prepared to go to court over the issue and to seek prosecution of individuals if they are found to have violated the Anti-Deficiency Act.